The advancement of wireless communication technologies and networking systems has provided users of such technologies a variety of communication services. Namely, wireless communication services provide, amongst others, voice, email, internet, messaging and data communications between various wireless, network and wireline devices connected directly or indirectly to any one or more of numerous existing wireless networks in operation around the globe.
One type of wireless service gaining popularity due to its wide applications and increasing availability is Location-Based Services (LBS). The LBS can be used in various applications and conditions, such as emergency assistance, criminal tracking, GIS (Geographical Information System), traffic information, vehicle navigation and tracking, as well as various location-dependent advertising and marketing systems and methods. In each case, the LBS uses the mobile user's position to provide the service in question. This position can be determined and calculated using various methods and systems including network-based positioning methods such as Cell-ID, E-OTD (Enhance Observed Time Difference), AFLT (Advanced Forward Link Trilateration), EFLT (Enhanced Forward Link Trilateration), TDOA (Time Difference of Arrival), and AOA (Angle of Arrival), external methods including GPS (Global Positioning System) and A-GPS (Assisted GPS), and hybrid methods combining at least two of the above.
Network-based methods generally use the signals communicated between a mobile device and one or more network tower communicating therewith to calculate the position of the mobile device. Generally, the position is computed by the network and the position accuracy is dependent on the network coverage in the area. In other words, a user of a LBS implemented using a network-based positioning method will be better served in an area densely covered by the network supporting the user device and LBS, rather than in an area sparsely covered by the supporting network.
GPS on the other hand operates independently of the radio and cellular communication networks. The GPS is a worldwide navigation and positioning system which determines the location of an object on earth by using a constellation of twenty-four (24) GPS satellites in orbits at an elevation of approximately 20 000 Km above Earth. The satellites broadcast specially coded signals that can be processed in a GPS receiver. Generally, signals from at least four (4) satellites are needed to compute the receiver's position in 3D, namely computing the receiver latitude, longitude, altitude and synchronization to GPS time.
Generally, the position of the GPS receiver is triangulated by calculating the propagation time of signals between the satellites and the receiver. The coded signals transmitted by the satellites are replicated in the GPS receiver. If the satellite and receiver clocks are properly synchronized, the replica code may be shifted in time until satellite and replica code synchronization is optimized. The time shift required for code synchronization thus provides the propagation time, and ultimately the distance between the receiver and the satellite. The calculated propagation times and attributed distances, otherwise termed pseudoranges due to the lack of perfect synchronicity between the satellites and the receiver, can be used to calculate the position of the receiver, generally within 10 meters, and the user clock offset, generally within 0.1 μs.
Since GPS relies on the reception of satellite signals, a GPS receiver relies upon having a reasonably clear view of the sky. Consequently, a GPS-based LBS will be far less efficient indoors, or even in a dense urban setting where signal interference and multiple reflections may drastically reduce the efficiency and accuracy of GPS measurements. Furthermore, since a stand-alone GPS receiver does not generally provide a communication link with any public or proprietary wireless communication network, the GPS receiver will be coupled with an appropriate mobile communication device (MCD) to communicate its position to an LBS platform and application server through a supported wireless network.
A conceptual prior art GPS-based LBS system is illustrated in FIG. 1. A client 10, acquires GPS positioning data using a GPS receiver 12 in communication with, in general, at least four (4) GPS satellites 14. The calculated positions are passed through the client application 16, and transmitted, using an appropriate MCD 18 in communication with a wireless communication network, to an application server 20. The wireless communication network may comprise such networks as, for example, a GSM/GPRS wireless communication network, a CDMA wireless communication network, a TDMA wireless communication network, a WCDMA wireless communication network, etc. In general, the wireless communication network will comprise plural base stations 22, each comprising at least one base transceiver station (BTS) 23 and a base station controller (BSC) 24 for direct communication with the MCD 18, and a mobile switching center 25 directing the communicated data to the application server through a core network 26. The application server 20 can then extract the data from the network 26. Communication from the application server 20 to the client 10 is also possible in the reverse order.
In order to improve GPS coverage, an LBS may opt to implement an A-GPS solution. The A-GPS technology concept combines GPS data acquired by a mobile GPS receiver and a fixed GPS receiver. In essence, the A-GPS concept is similar to DGPS (Differential GPS) wherein GPS data gathered by the fixed receiver is used to improve GPS positioning of the mobile unit. Yet, unlike DGPS, which is usually implemented to improve mobile positioning accuracy, A-GPS is generally used to improve the coverage of the mobile GPS receiver, and thus provide a better service.
A conceptual prior art A-GPS network, as illustrated in FIG. 2, includes a client 28 comprising an A-GPS receiver 30 that also acts as a MCD, an A-GPS server 34 with a reference GPS receiver 36 that can simultaneously “see” the same satellites 38 as the client 28, and a wireless network infrastructure comprising plural base stations 40 and a MSC 42. The A-GPS server 34 can obtain from the MSC 42 the client's position (up to the level of the cell and sector), and at the same time monitor the signals from the GPS satellites 38 seen by the client 28. Consequently, the A-GPS server 34 can predict to a certain accuracy the GPS signals received by the client 28 for any given time, and assist the A-GPS receiver 30 in GPS signal acquisition by providing various position-dependent acquisition parameters, such as the Doppler shift of the GPS signals, to the client 28. Consequently, a client 28 comprising an A-GPS receiver 30 can detect and demodulate weaker signals than conventional GPS receivers as part of the acquisition and processing workload is taken by the reference receiver 36.
An A-GPS receiver, as in 30, can thus provide greater coverage to a mobile user than a single GPS receiver, working even indoors and in dense urban areas. Furthermore, as a connection is maintained between the A-GPS receiver 30 and the A-GPS server 34, GPS data may be transmitted to the A-GPS server 34 for processing, thereby further reducing the processing load on the client 28. Alternatively, the client may be equipped with a full A-GPS receiver 30 for full GPS processing. The computed positions can then be transferred to the A-GPS server 34 over the wireless link already established therewith for communication of acquisition parameters therefrom. In either case, the positioning data is accessible to the application server 46 through the core network 44.
In general, an A-GPS can be implemented in a variety of wireless communication networks. For example, the European GSM (Global System for Mobile Communications) standards GSM 03.71, 08.71 and 09.31, the North American GSM standard GSM 04.35, the CDMA standards IS-801-1 and IS-801-A, the TDMA standard TIA/EIA-136, as well a other relevant standards documents discuss provisions for such systems. Newer and evolving networks such as UMTS and WCDMA, leading the way to 3G (third generation) networks, can also provide A-GPS services. Other networks, possibly operating in other communication bands, may also implement their own A-GPS system and provide A-GPS coverage to their respective clients.
As stated hereinabove an LBS can be used in various applications and conditions. For example, an LBS may be used for vehicle tracking and navigation, namely in the context of emergency assistance and emergency response vehicles. An LBS of this type is often referred to as an automatic vehicle location (AVL) system, wherein tracking and navigation information is provided by a server application to plural clients mounted or carried within the vehicles in the system.
The prior art AVL client consists of an AVL application, a GPS or an A-GPS receiver and a wireless communication transceiver in communication with the server application or AVL server. The AVL server, which gathers client position information, uses these positions to track and provide navigation instructions to the clients as part of a dispatch center. The user, which receives instructions from the dispatch center, may also visualize navigation information, such as client positions, destinations, and other related positional information on a client display, or simply follow voice or text instructions transmitted thereto.
With reference now to FIG. 2, if the client 28 of an AVL system user is equipped with an A-GPS receiver 30, the position of the client 28 will be determined through the A-GPS network and automatically made available to both the client 28 and an application server 46 in communication with the A-GPS server 34. In general, GPS position determination is inherent in the communication protocols of an A-GPS network. In other words, neither the AVL client application 48 nor the AVL application server 46 need send the positioning data through the network as the client position is implicitly made available to both parties by the A-GPS network communication protocols. As discussed hereinabove, the mobile positions are calculated using both data from the mobile device 28 and data from the A-GPS server 34. Consequently, positions are generally automatically provided to both the mobile device 28 and the A-GPS server 34 through the network's own communication protocols. The AVL application server 46, without communicating directly with the clients, can access the client positions from the A-GPS server 34.
With reference now to FIG. 1, if the client 10 of an AVL system user is otherwise only equipped with a GPS receiver 12, the AVL client application 16 will gather positioning data from the GPS receiver 12 and transmit the data to the AVL application server 20 through an appropriate communication link. In this scenario, data is not provided to the application server 20 directly by the wireless network as positioning determination is not implicit to the network's communication protocol, as it is for the A-GPS system illustrated in FIG. 2.
One particular limitation of prior art AVL systems, and generally of LBS systems, is the lack of consistent positioning coverage as a user commutes from one coverage area to another. For instance, a user equipped with a GSM based A-GPS mobile device may not get full coverage in a CDMA rich area. Alternatively, the same user may travel to an area where a GSM network is operative, but where an A-GPS service is not provided. Furthermore, as network structures and technologies evolve, a user equipped with state-of-the-art instrumentation may not get satisfactory coverage in areas still served by legacy networks, and vice versa. For example, some digital MCDs were not developed to operate within analogue networks, or again, are not compatible with competing digital networks. Consequently, though the above user may be well equipped in one area, the equipment may lose positioning accuracy and efficiency in another area, or lose coverage entirely. For this reason, users of a LBS, or for example an AVL system, wherein consistent knowledge of positioning information is of great importance, and wherein the loss thereof could have serious consequences, may be forced to carry plural MCDs supported by various networks to ensure consistent coverage.
For example, AVL systems used in emergency vehicle dispatch centers and other such AVL systems for vehicle tracking and navigation may benefit from plural radio and GPS coverage. Alternatively, an LBS for criminal tracking may also require a reliable and consistent tracking mechanism; however, prior art LBS systems are not configured to address plural GPS and communication resources. In general, prior art LBS systems are constructed to operate using a single GPS input for each LBS client. Consequently, prior art LBS clients may get confused in the presence of plural GPS sources, particularly in the presence of both GPS and A-GPS sources where data may or may not need to be sent by the client application to the application server.
Consequently, a GPS data management module for a LBS system, for example an AVL system, is needed to provide increased radio and GPS coverage options and versatility to the LBS. Example embodiments of the invention, described herein and with reference to the appended illustrative drawings, provide a GPS data management module that helps overcome drawbacks of prior art LBS systems.